Electromechanical acoustic noise source

ABSTRACT

An acoustic noise source wherein the noise is generated electromechanically by the rotation of a mass within and in rolling contact with a slotted thin-walled cylinder.

United States Patent 91 McCoy et al.

mlMarch 13, 1973 ELECTROMECHANICAL NOISE SOURCE Inventors: Bernard J.McCoy, Herndon, Va.;

Frank 0. Rans, Rockville, Md.

ACOUSTIC Assignee: The United States of America as represented by theSecretary of the Navy Filed: Dec. 3, 1970 Appl. No.: 94,925

US. Cl. ..340/8 R, 116/27, 116/137 R, 181/05 AG, 340/5 D Int. Cl. ..H04b11/00 Field of Search... ..340/5 D, 5 R, 8 R, 12 R; 181/05 R, 0.5 A, 0.5AG; 116/27, 137 A, 137 R References Cited UNITED STATES PATENTS Hayes eta1. ..181/0.5 Odenweller et al. ..116/27 Douglas et al. .181/0.5 A XFreeman et a1 ..116/27 Primary ExaminerRichard A. Farley AtwrneyR. S.Sciascia, Q. E. Hodges and R. M.

Wohlfart An acoustic noise generated electromechanically by the rotationof a mass within and in rolling contact with a slotted thinwalledcylinder.

ABSTRACT source wherein the noise is 14 Claims, 3 Drawing Figures 'SHEEI10F 2 INVENTORS' BERNARD J. MQCAY 0. RAMS A770 NEYS Fr? 1 BYPATENTEDMAR13 ma PATENTEUMAR 13 1975 SHEET 2 UF 2 FIG. 2.

IN VEN TORS BE RIVA/1 0 J. MC CA Y ATTONEYS ELECTROMECIIANICAL ACOUSTICNOISE SOURCE The invention described herein may be manufactured and usedby or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION 1. Field of the Invention Sonar systemswhether used on submarine or surface ships have to be calibrated by useof an acoustic noise source. The noise source is usually electronic andcan be designed to operate over a desired frequency span.

2. Description of the Prior Art At the present, state-of-the-art devicesfor generating noise for sonar calibration are largely piezoelectric andsome magnetostrictive.

The piezoelectric devices utilize crystal transducers. These devices arenot flexible in their coverage of the frequency spectrum. Therefore, toachieve lower frequencies the transducers must get larger. To insureproper coverage of the frequency spectrum four separate transducers,each tuned to a portion of the spectrum, are used. Each transducerrequires its own power amplifier, signal generating, sloping network andother equipment. In addition, to size and complexity, cost becomesprohibitive. Also, the power output in the low frequency end of thespectrum is low, and the spectrum is irregular.

SUMMARY OF THE INVENTION This invention provides an electromechanicalnoise source which utilizes a slotted cylinder with a rotating masstherein. The cylinder isthin walled and the contact between the rotatingmass and the interior of the cylinder, as the mass passes from slottedsection to slotted section, creates acoustic power at the excitationfrequency, its harmonics, and the ring frequency of the cylinder. Theexterior of the cylinder is coated with a rubber material having lowpass filter characteristics, thereby attenuating the excessive higherfrequencies. The ability of the calibration source to be tuned to afrequency spectrum by choosing a specific number of slots in thecylinder or by varying the RPM of the rotating mass allows a muchsmaller and versatile unit to be made at a fraction of the cost ofprevious devices.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of theinvention with some parts cut away for clarity.

FIG. 2 is longitudinal view of the invention, mostly in section withsome parts broken away for clarity.

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2.

DESCRIPTION OF THE INVENTION Referring now to the drawings the acousticnoise source is indicated generally at 10. A casing 12 completelyencloses the calibration source 14 and the power section 16.

The casing 12 has an elongated relatively thin walled cylinder 18 thatis closed on one end by a cap 20. The cap 20 has an O-ring 22 that sealson the inner circumference of the cylinder 18 to produce a water tightseal therebetween. The cap is held in position by a series of screws 24extending through the cylinder 18 and into the cap 20.

The cylinder 18 has a plurality of slots 26 cut into the circumferencethereof along the longitudinal axis. The slots 26 are positioned nearthe end of the cylinder adjacent the cap 20 and divide the circumferenceof the cylinder into longitudinally extending beams 28. To maintain thewater tight integrity of the cylinder 18 a collar of polyethylene 30 ismolded around the circumference to overlie the slots 26. Thus the watertight cylindrical casing 12 is formed, with a series of beams 28 alongthe wall thereof at the end of the casing surrounding the calibrationsource 14.

The calibration source 14 rotates within the cylinder 18, across thebeams 28 and has a main spindle 32 mounted concentric with thelongitudinal axis of the casing. The spindle 32 is cylindrical inconfiguration and has a circumference somewhat less than the innerdiameter of the cylinder 18 with a center bore 34 extending through thecenter thereof. A pair of annular grooves 36 and a pair of annularnotches 38 are cut into the circumference thereof, leaving a series oflands 40, 42 and 44 therebetween. A pair of aligned U-shaped notches 46and 48, spaced apart 180 on the circumference, are cut into the lands40, 42 and 44 whose function will be described hereinafter.

A pair of end caps 50, having the same circumference as the spindle 32,are attached to the ends thereof by a series of screws 52. The end caps50 have opposed pairs of bearings 54 and 56, mounted on their innerface, in alignment with the bottom of the notches 46 and 48,respectively, to provide an axis of rotation for a pair of rotatingmasses 58.

The pair of rotating masses 58 are identical and have a main shaft 60with a pair of annular rings 62 fixed thereon in spaced relation tocoincide with the annular grooves 36. The main shafts 60 of each mass 58has a non-metallic section 64 on the ends thereof. The section 64 isusually Teflon and acts to reduce shear friction generated by therotation of the mass 58. An end cap 66 is fixed on the end of eachsection 64 to be received in the pairs of bearings 54 and 56. When themass 58 is in position and journalled for rotation in the bearings 54and 56, the main shafts 60 extend through the notches 46 and 48 with therings 62 received in the grooves 36 and in rolling engagement with theinner surface of the cylinder 18. A drive shaft 68 is received in thecenter bore 34 of the spindle 32 and fixed thereto by pins 70 totransmit the driving rotation movement thereto. The drive shaft 68 has asocket 72 on the free end thereof to receive the motor shaft from thepower section 16.

The power section 16 has a DC motor 74 whose shaft 76 is received in thesocket 72 and fixed thereto by means of a pin 78. The motor 74 has apair of circular plates 80 and 82 attached to the ends thereof by aseries of screws 84. The plates 80 and 82 have approximately the samediameter as the inner diameter of the cylinder 18 and are adapted toslide therein. The plate 82 is attached to a cap 86 by means of screws88 and spacers 90. The cap 86 is similar to the cap 20 and has an O-ring92 to seal the cap to the inner circumference of the cylinder 18 toproduce a water tight seal therebetween. The cap is held in position bya series of screws 94 extending through the cylinder 18 and into the cap86. The wires 96, from the motor 74 extend through an opening 98 in thecap 86. Any convenient means can be used to effect a water tight sealfor the passage of the wires 96 through the opening 98 in the cap 86. Acup-shaped member 100 is shown threadedly engaged in the opening 98 witha threaded gland fitting 102 to seal the wires 96.

Thus, the entire unit maintained with water tight integrity whencompletely assembled. To complete the structure of the invention, theentire casing is wrapped with a layer of material 104. The material 104should be a rubber based product with air pockets therein. A commercialavailable produce RAL has been found to serve the purpose since it actsas a low pass filter for attenuating the excessive higher frequenciesproduced by the calibration source. The RAL covering 1043 can be held inposition by any convenient means such as the clamps 106 shown in thedrawing.

in operation, DC voltage is supplied to the motor 74 which turns'thespindle 32 through the motor shaft 76 and the drive shaft 68. Theturning of the spindle 32 causes the masses 58 to rotate due to therolling contact of the annular rings 62 with the inner surface ofcylinder 18. As the rotating masses 58 move over the slots 26 and beams28 an impact occurs on each beam. This impact causes a displacement ofthe beam and a corresponding displacement of the water, creatingacoustic power at the excitation frequency, its harmonies, and the ringfrequency of the cylinder.

The frequency of the excitation is given by:

where N motor RPM t number of slots D ID of cylinder d= OD of rotatingmass The ring frequency is given by:

where:

C= speed of sound in cylinder wall d diameter of cylinder In addition,to controlling the excitation frequency the longitudinal slots 26 in thecylinder 18 serve to govern the amplitude of the transmitted spectrum byacting as a fixed-fixed beam in the lower frequency range of thespectrum between 100 and 800 Hz. This increase averages db compared to anon-slotted cylinder, while effectively decoupling the upper frequencyrange of the spectrum between 1.6 and 10 kHz, at 6 db. Also, the RALcovering 104 acts as a low pass filter to attenuate the excessive higherfrequency above 1 kHz an additional 6 db.

As can be seen, a relatively simple and inexpensive noise source isprovided for calibrating sonar units that has a wide range of frequencyproduction from a single unit. The unit is also smaller and more rugged.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. IT is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

it. An acoustic noise source, comprising:

a casing;

a power source mounted within the casing;

a calibration source within the casing connected to the power source tobe rotated thereby and to impact with the casing to produce acousticnoise within a selected exitation frequency spectrum;

means for selecting the spectrum; and

means for attenuating the spectrum.

2. A device according to claim 1 wherein said casing is a thin walledcylinder with closure members at each end thereof.

3. A device according to claim 2 where at least two longitudinal slotsare cut into the cylinder near one end thereof.

4. A device according to claim 3 wherein a collar of elastic material ismolded around the slots to maintain the closed cylinder water tight.

5. A device according to claim 4 wherein the cylinder and collar arecovered with an expanded rubber material.

6. A device according to claim 1 wherein the calibration source is arotating member within the casing and in contact therewith.

7. A device according to claim 6 wherein the rotating member includes aspindle and two rotating masses journalled for rotation thereon.

8. A device according to claim 7 wherein the spindle is driven by thedrive means and the rotating masses are in rolling contact with theinterior of the casing.

9. A device according to claim 1 wherein said casing includes a thinwalled cylinder with at least two longitudinal slots at one end thereof.

10. A device according to claim 9 wherein the calibration sourceincludes a rotating mass in rolling contact with the interior slottedend of the cylinder.

11. The device of claim 1 wherein the means for selecting the exitationfrequency spectrum comprises:

a plurality of slots longitudinally provided in the easing for forming aplurality of substantially uniform longitudinal beams therebetween.

12. The device of claim 11 wherein the means for attenuating thespectrum comprises:

a layer of air pocketed rubber based material wrapped about the casing.

13. An acoustic noise source, comprising:

an elongated cylindrical casing;

a plurality of slots longitudinally provided in the easing for forming aplurality of substantially uniform longitudinal beams therebetween;

a power source mounted within the casing;

a calibration source connected to the power source to be rotated therebywithin the cylinder and to impact with the beams to produce acousticnoise within a selected frequency spectrum; and

layer of air pocketed rubber based material wrapped about the casing forattenuating the spectrum.

14. An acoustic noise source, comprising:

an elongated cylindrical casing;

a plurality of slots longitudinally provided in the casing for forming aplurality of substantially uniform longitudinal beams therebetween;

a power source mounted within the casing;

a calibration source connected to the power source to be rotated therebywithin the cylinder and having an outside diameter provided to impactwith the inside diameter of the casing at the beams to produce acousticnoise within a selected exitation frequency spectrum as represented bythe formula: F=NtD/60d, where N is the RPM of the power source, t is thenumber of slots, D is the inside diameter of the cylinder and d is theoutside 5 diameter of the calibration source.

* t t t i

1. An acoustic noise source, comprising: a casing; a power sourcemounted within the casing; a calibration source within the casingconnected to the power source to be rotated thereby and to impact withthe casing to produce acoustic noise within a selected exitationfrequency spectrum; means for selecting the spectrum; and means forattenuating the spectrum.
 1. An acoustic noise source, comprising: acasing; a power source mounted within the casing; a calibration sourcewithin the casing connected to the power source to be rotated therebyand to impact with the casing to produce acoustic noise within aselected exitation frequency spectrum; means for selecting the spectrum;and means for attenuating the spectrum.
 2. A device according to claim 1wherein said casing is a thin walled cylinder with closure members ateach end thereof.
 3. A device according to claim 2 where at least twolongitudinal slots are cut into the cylinder near one end thereof.
 4. Adevice according to claim 3 wherein a collar of elastic material ismolded around the slots to maintain the closed cylinder water tight. 5.A device according to claim 4 wherein the cylinder and collar arecovered with an expanded rubber material.
 6. A device according to claim1 wherein the calibration source is a rotating member within the casingand in contact therewith.
 7. A device according to claim 6 wherein therotating member includes a spindle and two rotating masses journalledfor rotation thereon.
 8. A device according to claim 7 wherein thespindle is driven by the drive means and the rotating masses are inrolling contact with the interior of the casing.
 9. A device accordingto claim 1 wherein said casing includes a thin walled cylinder with atleast two longitudinal slots at one end thereof.
 10. A device accordingto claim 9 wherein the calibration source includes a rotating mass inrolling contact with the interior slotted end of the cylinder.
 11. Thedevice of claim 1 wherein the means for sElecting the exitationfrequency spectrum comprises: a plurality of slots longitudinallyprovided in the casing for forming a plurality of substantially uniformlongitudinal beams therebetween.
 12. The device of claim 11 wherein themeans for attenuating the spectrum comprises: a layer of air pocketedrubber based material wrapped about the casing.
 13. An acoustic noisesource, comprising: an elongated cylindrical casing; a plurality ofslots longitudinally provided in the casing for forming a plurality ofsubstantially uniform longitudinal beams therebetween; a power sourcemounted within the casing; a calibration source connected to the powersource to be rotated thereby within the cylinder and to impact with thebeams to produce acoustic noise within a selected frequency spectrum;and a layer of air pocketed rubber based material wrapped about thecasing for attenuating the spectrum.